I am merely speculating - (although there may be a possibility that I should not have finished off all the wine!

) that I seem to recall that there was a period when
Boler was making some that were 100% symetrical, so - since those front reflectors are the same "frenched in" appearance as the back
lights.....
I believe that they were trying to sell trailers to parts of the world where vehicles get driven from the "wrong side" and putting the bodies on the frame backwards to get the door properly oriented (on the left side for right-hand drive cars) - so having the frenched-in Taillights mirrored at the other end would be sensible.